1. Field of the Invention
The present invention relates primarily to valves, especially those used in post-mix beverage dispensers.
2. State of the Art
Post-mix beverage dispensers control the flow of two liquids in separate conduits. For most soft drinks, the liquid in one conduit is water saturated with carbon dioxide. Flavored syrup concentrate flows through the other conduit. Ideally, valves controlling the flow of the two components through the separate conduits open simultaneously. Flow regulators for each liquid maintain a fixed flow rate so that the components mix at the predetermined ratios. The conduits lead to a mixing chamber in which the two liquids combine just before or as they leave the valve system. When dispensing is complete both valves close, and fluid flow through both conduits stops.
To maintain proper flow for both components, the valves must be fully opened or fully closed. If either valve has some intermediate position, the valve system may dispense more of one component than the other. This results in the all too common watered down or too syrupy dispensed soft drink. Mechanical valves that do not immediately fully open and fully close are most subject to this problem. This is especially true when the person using the soft drink dispenser attempts to dispense small volumes of the soft drink to fill a cup to the top, a process called "teasing."
Present day dispensers usually use electrical solenoid valves. Electrically activated valves can be opened and closed simultaneously so that flow through both conduits start and stop together.
Solenoid valves generally exhibit high pressure loss and are expensive, however. In high pressure, high flow systems, the solenoid valves must be large enough to overcome system pressure so that they can close or open very fast. If the solenoid valves do not open or close very fast, there can be substantial flow while the valves are opening or closing. When flow occurs while either valve is partially open, the percentage of the two components in the final soft drink product may change. This is especially a problem when the valves are teased or opened and closed several times during the dispensing of one drink.
Brown, U.S. Pat. No. 4,266,726 (1981) and Fuerst, U.S. Pat. No. 3,540,476 (1970), are examples of beverage dispensers using solenoid valves.
Mechanical valves also exist. If mechanical valves are to have fully opened or fully closed positions and avoid intermediate, partial flow conditions, they usually have complicated over-center activation systems. These are usually quite costly to manufacture and require a high actuation force. These mechanical valves can be electrically activated, but the electrical activation is usually slow and has a relatively high power requirement. This is disadvantageous in a liquid dispenser because higher electrical power devices are more expensive and are not energy efficient.
Solenoid and mechanical valves currently in use today often require field adjustment. That is, a technician often must adjust the valves after they are installed to obtain optimum performance. The valves also require service. Additional service requirements are costly for the manufacturer and owner of beverage dispensers.